1. Field of the Invention
The invention relates to a data recovery device and method. Particularly, the invention relates to a data recovery device and method for an optical storage system.
2. Description of Related Art
When an optical storage system reads a radio frequency (RF) signal, it is liable to be influenced by factors such as inter-symbol interference (ISI), electrical delay, aging of dyes on a disc, or scratching surface of the disc to cause a poor recognition, so that a recognition degree of the RF signal is influenced. To avoid the above problem, the RF signal read by an optical pickup head has to be processed by a data recovery device, so that the system can obtain a modulation signal and a clock signal representing the original data.
Generally, most of the existing data recovery devices first convert the RF signals into digital sampling data points, and then compensate the RF signal with an excessively short period length by increasing gain values of the sampling data points. For example, in the existing data recovery device, the RF signal with an excessively short period length is amplified, and the RF signal with a relatively long period length is almost maintained to it original magnitude. Then, the existing data recovery device fetches retiming data points with reference of compensated sampling data points, and recovers the retiming data points to a modulation signal.
However, when the RF signal compressed (or burned) on the disc is abnormal due to wearing of a mold or unevenness of a burn power, a common phenomenon thereof is as that shown in FIG. 1, and in FIG. 1, a dotted line represents sampling data points obtained after the RF signal is sampled, and circles represent the returning data points. Referring to a retiming data stream RTO11 at an upper portion of FIG. 1, a signal with a period length of 3T is generally amplified, so that the system recovers the retiming data stream RTO11 to signals of 4T, 3T and 4T, wherein T refers to a time interval of one channel bit. However, when the compensated 3T signal is still excessively small, as that shown by a retiming data stream RTO2 at a lower portion of FIG. 1, a minimum point of the 3T signal cannot be lower than a reference level. Therefore, the system misjudges the retiming data stream RTO12 as a signal of 11T (4T+3T+4T).
In other words, regarding the abnormal RF signal (for example, the RF signal with an excessively short period length), the existing recovery device can only compensate the RF signal by increasing the gain value. However, when the gain value is not great enough, the optical storage system still cannot obtain the original data. Moreover, the greater the gain value is, the more obvious the RF signal with a relatively long period length is influenced, so that the normal RF signal can be influenced.